The present invention relates to a pressure control valve, and, more particularly, to an electromagnetic pressure control valve capable of controlling fluid pressure in response to an electric signal.
Pressure control valves are represented by a diaphragm type pressure control valve wherein the surface of the diaphragm receives feedback pressure and a spool type pressure control valve wherein the end surface of the spool receives feedback pressure. The present invention relates to an electromagnetic pressure-control valve of the spool type.
The spool type electromagnetic pressure-control valve is usually designed in such a manner that a load caused by the electromagnet, a spring load, and an output pressure feedback load act on a spool valve which slides in a valve sleeve having a supply port, an output port, and an exhaust port. Its structure is arranged such that the output pressure is controlled to a level which corresponds to the electric signal supplied to the electromagnet portion by arranging a balance among the above-described loads (see Japanese Patent Laid-Open No. 60-52509).
The pressure control valves of the type described above are arranged in such a manner that the operation of the spool valve is stabilized by feeding back the output pressure to either end surface of the spool valve, where a feedback oil passage is formed in the outer portion of a valve sleeve of a pressure governing valve portion thereof in order to feed back the output pressure.
However, the above-described structure of the conventional pressure control valve arranged such that the feedback oil passage is formed in the outer portion of the valve sleeve of the pressure governing valve portion requires that the overall size of the pressure control valve to be enlarged by a degree corresponding to the feedback oil passage thus formed. Furthermore, the number of manufacturing steps is increased by forming the feedback oil passage.
Furthermore, the structure arranged such that the output pressure is fed back through the feedback oil passage thus formed does not produce a satisfactory damping effect. Therefore, it is difficult to stably and reliably operate the spool valve, and another problem of operation noise such as so-called "buzz" also arises.